Production of hydrocarbons from subterranean reservoirs below a seabed has previously been described. In such operations, a floating drilling or/and production vessel is positioned above a subsea wellhead, and a riser extends between the vessel and the wellhead. Over the years, technological advances have made it possible to extract hydrocarbons from subsea reservoirs at ever increasing water depths; operations at water depths exceeding 3000 meters is not uncommon today.
A drilling riser comprises a number of successive sections (often referred to as “riser joints”) whose adjacent ends are connected on board the vessel as the riser is being lowered towards the wellhead. A riser joint is typically made up of a main pipe and external auxiliary lines, all of which have connectors at each respective end. The main pipe is configured to convey drilling fluid, while auxiliary lines referred to as “kill and choke lines” are used to circulate fluids between the drilling vessel and a blow-out preventer (BOP) on the subsea wellhead, in a manner which is known in the art.
When operating in water depths of around 3000 meters and beyond, the riser mass (that the floating vessel must support) is considerable. Drilling operators and oil companies are therefore always looking for ways to reduce the size and weight of the riser joint components. Because some of the auxiliary lines (notably the kill and choke lines) convey fluids that are under considerable pressure, their wall thicknesses must, however, have a certain magnitude. It is therefore of particular interest to design the riser connector so that the loads caused by the main pipe and the auxiliary lines are transferred between the riser joints in an efficient manner, while the connector mass is optimized.
The prior art includes U.S. Pat. No. 4,043,575 which describes a connector for use between two riser pipes having a pin fitting at the end of one pipe. The pin fitting forms a portion of the connector. An end sleeve on the pin fitting has a cylindrical exterior surface and a first peripheral flange with upper and lower normal surfaces. A box fitting is at the end of the other pipe and has an end box with a cylindrical inner surface engaging the cylindrical exterior surface of the pin fitting. A second peripheral flange on the box fitting has upper and lower normal surfaces and is adapted to abut the first flange. An annular nut is rotatable about the flanges and has interior threads engageable with exterior threads on a collar rotatable around the box fitting and abutting the second flange. An inturned, interrupted nut flange on the nut overlies the first flange, which is also interrupted. The nut flange and the first flange can be relatively rotated to pass each other axially or to prevent such an axial movement. The nut and collar can be held in any of several relatively rotated positions by a bolt and slot connection, and the collar is held by a bolt against turning on the box fitting. Both fittings carry adjustable support rings for auxiliary pipes.
The prior art also includes GB 2 320 541 which describes a riser connector having respective tubular members connected to adjacent ends of riser pipes in an end-to-end relation and having locking grooves about their adjacent ends locked by a split lock ring surrounding the adjacent ends of the tubular members. A support plate extends laterally from each tubular member, mounting pipes (which may be choke and/or kill lines) to sealably interfit with one another upon movement of the tubular members into an end-to-end relation. The pipes are directly locked to one another to prevent vertical separation independently of locking of the tubular members in an end-to-end relation. The locking is by transverse bolts operated by levers. The lock ring is moved between locking and unlocking positions via a cam ring having tapered conical cam surfaces thereabout for slidable engagement with follower surfaces about the lock ring.
The prior art also includes U.S. Pat. No. 4,487,434 which describes a coupling for riser pipe sections and associated parallel choke and kill line pipe sections, where one riser pipe section is inserted in a second riser pipe section. One of the riser pipe sections includes a threaded male end which has at least two sets of continuous threads. A female union box carried on the other riser section includes at least two sets of continuous threads interengaged with the sets of threads on the male end, the respective sets of threads being axially and radially spaced from each other, the union box engaging the other riser pipe section to prevent the sections from moving axially relative to each other. The sections are provided with a fluid tight seal and choke and kill line sections are also penetratingly joined and supported by the riser pipe sections.
The prior art also includes U.S. Pat. No. 5,992,893 which describes a riser connector wherein an upper plate is carried by an upper riser member and a lower riser plate is carried by a lower riser member of an upper connector, and upper and lower riser plates and are similarly carried by the upper and lower riser members of the second connector. The plates extend outwardly from the riser members so as to support conduits connected to the ends of the auxiliary line joints which extend along the sides of the riser pipes. The lower end of an upper conduit of the upper connector is thus supported by the upper plate of the upper connector, while the upper end of the lower conduit thereof is supported by the plate of the upper connector.
The prior art also includes WO 2011/104629 which describes a connector for assembling two riser pipe sections for offshore well drilling operations. The connector comprises a first main tube element having as an extension a male connector element provided with a male flange pierced by at least one orifice wherein an auxiliary tube element is secured, and a second main tube element having as an extension a female connector element provided with a female flange pierced by at least one orifice wherein a second auxiliary tube element is secured. The male connector element fits into the female connector element so as to connect the two main tube elements and the two auxiliary tube elements. A locking ring assembles the male flange and the female flange, the locking ring being mounted mobile in rotation on the outer surface of the male flange, and the locking ring cooperating with the outer surfaces of the male and female flanges. The locking ring can be locked in translation by an axial shoulder provided on the male flange, and the ring can be provided with tenons that cooperate with the tenons arranged on the outer surface of the female flange.
The prior art also includes U.S. Pat. No. 4,280,719 which describes a connector having two interfitting tubular elements and a locking ring with at least two staggered rows of locking lugs cooperating with corresponding locking lugs of one of the tubular elements. The locking lugs are inscribed in cylindrical surfaces having different radii, so that when the ring is inserted on the element, its lugs slide on the lugs of the first lug row of the element to a position where the lugs of each lug row of the ring can pass between those of a corresponding row of the element to form a plurality of bayonet couplings which can then be simultaneously locked.